I'm here. I can't define good, I'm a mere human like all you. I saw this questions and loved the way it spun my brain.
If I were to call you a name, or take something from you, or the fact that people argue shows that there is law we all should know. If you say "it's not fair" you assume some sort of law that I should agree with. Then I may make an excuse for doing what I did that made it not fair. I broke some unseen law.
Nor has it ever been good to betray a friend or be selfish. There is some unseen law we all try to follow. If you brake it your not good.
To answer my own question. No, we could not be able to be good without God. He told us what is good. You can fool your self into thinking there is no law but as soon as I say some thing mean to you, you would go back on this by saying "don't call me that, thats not nice"
Not only that, the very fact that we cannot even reason this question and it would go past a 1000 post with no conclusion also show that we humans don't have the ability to agree to a good. We end up saying, believe what you want and I'll believe in what I want. (Humanism) It turns up in chaos because our society will start to fall. No need for government or even rules just do what ever you want and try to be good? But my idea of good may differ. Turns in to a catch 22.